Messing around with linux PCI hotplug
Jan 25, 2012
Been playing around with PCI hotplug on linux (3.2.1 kernel from kernel.org), or rather, with the fakephp driver (fake PCI hot plug driver). The way it works is you load the fakephp driver, and this creates a bunch of directories in /sys/bus/pci/, one per PCI device (ok, per domain/bus/device/function ) and inside each directory is a “power” file. If you write 0 to the power file, that device is “hot unplugged”. Well, not really, but the driver entry points get called as if it were hot unplugged. It’s surprisingly difficult to find the documenation for this as most searches related to linux and pci hotplug return old stuff.
You can “re-hot-plug” the device back in by echoing a 1 into /sys/bus/pci/rescan.
Anyway, here’s an example of using the fakephp driver to simulate hot unpl
root@hermes:/sys/bus/pci# uname -r 3.2.1 root@hermes:/sys/bus/pci# pwd /sys/bus/pci root@hermes:/sys/bus/pci# ls devices drivers drivers_autoprobe drivers_probe rescan resource_alignment slots uevent root@hermes:/sys/bus/pci# ls slots root@hermes:/sys/bus/pci# modprobe fakephp root@hermes:/sys/bus/pci# ls slots 0000:00:00.0 0000:00:1b.0 0000:00:1d.2 0000:00:1e.0 0000:01:03.0 0000:01:03.3 0000:01:05.0 0000:00:02.0 0000:00:1d.0 0000:00:1d.3 0000:00:1f.0 0000:01:03.1 0000:01:03.4 0000:00:02.1 0000:00:1d.1 0000:00:1d.7 0000:00:1f.1 0000:01:03.2 0000:01:04.0
Above you see after loading the fakephp driver, the /sys/bus/pci/slots directory
is populated with device directories.
Now I go poking around looking for a network device (because I know the wired
network on my laptop isn’t currently plugged in, so if this doesn’t work, no
harm done so long as it doesn’t crash.)
root@hermes:/sys/bus/pci# lspci | grep -i net 01:04.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10) 01:05.0 Network controller: Intel Corporation PRO/Wireless 2200BG [Calexico2] Network Connection (rev 05)
So I see I have my Ethernet controller at 01:04.0. Now I start tailing
/var/log/messages so I can see the kernel’s response to my various pokings,
and I kick the unused ethernet adapter out of the system:
root@hermes:/sys/bus/pci# tail -n 0 -f /var/log/messages & [1] 4294 root@hermes:/sys/bus/pci# echo 0 > slots/0000\:01\:04.0/power root@hermes:/sys/bus/pci# Jan 25 21:28:05 hermes kernel: [13781.192061] 8139too 0000:01:04.0: PCI INT A disabled root@hermes:/sys/bus/pci# lspci | grep -i net 01:05.0 Network controller: Intel Corporation PRO/Wireless 2200BG [Calexico2] Network Connection (rev 05)
Yep, it’s gone. Now add it back in:
root@hermes:/sys/bus/pci# echo 1 > rescan root@hermes:/sys/bus/pci# Jan 25 21:28:23 hermes kernel: [13799.587819] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment Jan 25 21:28:23 hermes kernel: [13799.587841] pci 0000:01:04.0: BAR 0: assigned [io 0xd000-0xd0ff] Jan 25 21:28:23 hermes kernel: [13799.587855] pci 0000:01:04.0: BAR 0: set to [io 0xd000-0xd0ff] (PCI address [0xd000-0xd0ff]) Jan 25 21:28:23 hermes kernel: [13799.587865] pci 0000:01:04.0: BAR 1: assigned [mem 0xfe801000-0xfe8010ff] Jan 25 21:28:23 hermes kernel: [13799.587878] pci 0000:01:04.0: BAR 1: set to [mem 0xfe801000-0xfe8010ff] (PCI address [0xfe801000-0xfe8010ff]) Jan 25 21:28:23 hermes kernel: [13799.587888] yenta_cardbus 0000:01:03.0: CardBus bridge to [bus 02-01] Jan 25 21:28:23 hermes kernel: [13799.587896] yenta_cardbus 0000:01:03.0: bridge window [io 0x0001-0x0000] Jan 25 21:28:23 hermes kernel: [13799.587907] yenta_cardbus 0000:01:03.0: bridge window [io 0x0001-0x0000] Jan 25 21:28:23 hermes kernel: [13799.587919] yenta_cardbus 0000:01:03.0: bridge window [mem 0x00000001-0x00000000 pref] Jan 25 21:28:23 hermes kernel: [13799.587930] yenta_cardbus 0000:01:03.0: bridge window [mem 0x00000001-0x00000000] Jan 25 21:28:23 hermes kernel: [13799.594036] 8139cp 0000:01:04.0: This (id 10ec:8139 rev 10) is not an 8139C+ compatible chip, use 8139too Jan 25 21:28:23 hermes kernel: [13799.594093] 8139too 0000:01:04.0: PCI INT A -> GSI 20 (level, low) -> IRQ 20 Jan 25 21:28:23 hermes kernel: [13799.599565] 8139too 0000:01:04.0: eth0: RealTek RTL8139 at 0xd000, 00:11:d8:23:c2:86, IRQ 20 Jan 25 21:28:24 hermes kernel: [13799.639799] 8139too 0000:01:04.0: eth0: link down Jan 25 21:28:24 hermes kernel: [13799.644372] ADDRCONF(NETDEV_UP): eth0: link is not ready root@hermes:/sys/bus/pci# lspci | grep -i net 01:04.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10) 01:05.0 Network controller: Intel Corporation PRO/Wireless 2200BG [Calexico2] Network Connection (rev 05) root@hermes:/sys/bus/pci#
And now it’s back.
